Microfluidic chip features for optical and thermal isolation

ABSTRACT

A microfluidic chip includes microfluidic channels, elements for thermally and optically isolating the microfluidic channels, and elements for enhancing the detection of optical signal emitted from the microfluidic channels. The thermal and optical isolation elements may comprise barrier channels interposed between adjacently-arranged pairs of microfluidic channels for preventing thermal and optical cross-talk between the adjacent microfluidic channels. The isolation element may alternatively comprise reflective film embedded in the microfluidic chip between the adjacent microfluidic channels. The signal enhancement elements comprise structures disposed adjacent to the microfluidic channels that reflect light passing through or emitted from the microfluidic channel in a direction toward a detector. The structures may comprise channels or a faceted surface that redirects the light by total internal reflection or reflective film material embedded in the microfluidic chip.

RELATED APPLICATIONS

This application is a divisional of and claims priority to U.S. patentapplication Ser. No. 13/674,528, filed on Nov. 12, 2012, which is adivisional of and claims priority to U.S. patent application Ser. No.12/779,523, filed on May 13, 2010, now U.S. Pat. No. 8,329,117 issuedDec. 11, 2012, which claims the benefit of provisional application Ser.No. 61/178,233, filed May 14, 2009, each of which are incorporatedherein by reference in their entirety.

BACKGROUND

1. Field of the Invention

This invention relates to microfluidic devices having multiplemicrofluidic channels through which reaction materials flow and, morespecifically, to microfluidic devices having features for effectingoptical and thermal isolation of microfluidic channels in microfluidicdevices.

2. Description of Related Art

The detection of nucleic acids is central to medicine, forensic science,industrial processing, crop and animal breeding, and many other fields.The ability to detect disease conditions (e.g., cancer), infectiousorganisms (e.g., HIV), genetic lineage, genetic markers, and the like,is ubiquitous technology for disease diagnosis and prognosis, markerassisted selection, correct identification of crime scene features, theability to propagate industrial organisms and many other techniques.Determination of the integrity of a nucleic acid of interest can berelevant to the pathology of an infection or cancer. One of the mostpowerful and basic technologies to detect small quantities of nucleicacids is to replicate some or all of a nucleic acid sequence many times,and then analyze the amplification products. Polymerase Chain Reaction(“PCR”) is perhaps the most well-known of a number of differentamplification techniques.

PCR is a powerful technique for amplifying short sections of DNA. WithPCR, one can quickly produce millions of copies of DNA starting from asingle template DNA molecule. PCR includes a three phase temperaturecycle of denaturation of DNA into single strands, annealing of primersto the denatured strands, and extension of the primers by a thermostableDNA polymerase enzyme. This cycle is repeated so that there are enoughcopies to be detected and analyzed. In principle, each cycle of PCRcould double the number of copies. In practice, the multiplicationachieved after each cycle is always less than 2. Furthermore, as PCRcycling continues, the buildup of amplified DNA products eventuallyceases as the concentrations of required reactants diminish. For generaldetails concerning PCR, see Sambrook and Russell, Molecular Cloning—ALaboratory Manual (3rd Ed.), Vols. 1-3, Cold Spring Harbor Laboratory,Cold Spring Harbor, N.Y. (2000); Current Protocols in Molecular Biology,F. M. Ausubel et al., eds., Current Protocols, a joint venture betweenGreene Publishing Associates, Inc. and John Wiley & Sons, Inc.,(supplemented through 2005) and PCR Protocols A Guide to Methods andApplications, M. A. Innis et al., eds., Academic Press Inc. San Diego,Calif. (1990).

Real-time PCR refers to a growing set of techniques in which onemeasures the buildup of amplified DNA products as the reactionprogresses, typically once per PCR cycle. Monitoring the accumulation ofproducts over time allows one to determine the efficiency of thereaction, as well as to estimate the initial concentration of DNAtemplate molecules. For general details concerning real-time PCR, seeReal-Time PCR: An Essential Guide, K. Edwards et al., eds., HorizonBioscience, Norwich, U.K. (2004).

A number of commercial instruments exist that perform real-time PCR.Examples of available instruments include the Applied Biosystems PRISM7500, the Bio-Rad iCylcer, and the Roche Diagnostics LightCycler 2.0.

More recently, a number of high throughput approaches to performing PCRand other amplification reactions have been developed, for example,involving amplification reactions in microfluidic devices, as well asmethods for detecting and analyzing amplified nucleic acids in or on thedevices. Thermal cycling of the sample for amplification in microfluidicdevices is usually accomplished in one of two methods. In the firstmethod, the sample solution is loaded into the device and thetemperature is cycled in time, much like a conventional PCR instrument.In the second method, the sample solution is pumped continuously throughspatially varying temperature zones. See, e.g., Lagally et al.(Analytical Chemistry 73:565-570 (2001)), Kopp et al. (Science280:1046-1048 (1998)), Park et al. (Analytical Chemistry 75:6029-6033(2003)), Hahn et al. (WO 2005/075683), Enzelberger et al. (U.S. Pat. No.6,960,437) and Knapp et al. (U.S. Patent Application Publication No.2005/0042639).

Microfluidic chips are being developed for “lab-on-a-chip” devices toperform in-vitro diagnostic testing. The largest growth area is inmolecular biology where DNA amplification is performed in the sealedchannels of the chip. Optical detection devices are commonly used tomeasure the increasing amplicon product over time (Real Time PCR) or toperform a thermal melt to identify the presence of a specific genotype(High Resolution Thermal Melt). Exemplary disclosures related to theimaging of a microfluidic chip to measure the fluorescent product can befound in commonly-owned U.S. application Ser. No. 11/505,358 to Hassonet al. entitled “Real-Time PCR in Micro Channels” (U.S. Pat. Pub.2008-0003588) and U.S. application Ser. No. 11/606,204 to Hasson et al.entitled “Systems and Methods for Monitoring the Amplification andDissociation Behavior of DNA Molecules” (U.S. Pat. Pub. 2008-0003594),the respective disclosures of which are hereby incorporated byreference.

A general trend in in-vitro diagnostic microfluidic chips is to makethem smaller to conserve sample volumes, material cost, biohazard wastevolume, and to reduce thermal mass of the chip for faster PCR cycling.The down side of this size reduction, however, is the increaseddifficulty in isolating fluidic channels—both thermally andoptically—from each other.

Thermal separation of microfluidic channels is a more significant issueif the design has individual heaters for independent thermal cycling ineach channel. Independent thermal cycling does not necessarily mean thateach channel is driven on a different cycle, which is the extreme ofcontrol systems. Even if temperature cycling is performed in unison(i.e., simultaneously in all channels), if there is a separate,dedicated heating element for each channel, there is a potential thermalisolation issue. When one channel is higher or lower than a setpointtemperature, the control system needs to compensate locally. Deviationfrom setpoint temperature could be caused by varying wattages due to theheating element manufacturing tolerances or by greater heat loss whichcan occur at the edges of the microfluidic chip, thereby causing lowertemperatures in channels adjacent to the edge of the chip. The responseto changing inputs to individual heater elements must be isolated inorder to create an effective closed loop control. If a significantportion of energy from surrounding heater elements conducts into or outof the area of the heating element for which control input is beingadjusted, the response will be hard to predict because of thesurrounding influences. The control algorithms may be able to compensateif the surrounding influences were steady state, but in this case theyare also being actively controlled. This makes each channel lesspredictable and may make the system unstable. Improvingchannel-to-channel isolation by reducing or preventing thermal crosstalkbetween adjacent channels will improve control of the individual channeltemperatures.

Optical isolation of the microfluidic channels is also a problem forsome detection systems. As the size of microfluidic chips shrinks, thefluid volume within each channels is reduced, which consequently reducesemission signal levels. Also, as channels through which fluorescentindicators flow are also moved closer together this promotes emissionsignal crosstalk between adjacent channels. The clear glass or polymermicrofluidic chip creates light pipe paths between channels whichenables greater crosstalk.

When all channels are illuminated simultaneously, emitted fluorescentlight intensity is the critical parameter for detection. Even though theexcitation light is basically unidirectional from a single source, theemission light is omni-directional. It is possible, therefore, for onechannel to have no emission and light emitted from adjacent channelscrosses into the non-emitting one and through particle scattering orrefraction at the walls, some light is turned toward the detector. Thiscan elevate signal levels or give false signals.

Also, being omni-directional, most of the emission light does notpropagate in the direction of the detector. Much of the light istransmitted through the surface of the micro chip opposite the detector.Accordingly, the intensity of the emission light that actually reachesthe detector can be very small, making accurate measurementsproblematic.

This phenomenon is illustrated in FIGS. 1 and 2. FIG. 1 shows aschematic representation of a partial transverse cross-section of amicrofluidic chip 10 having a number of microfluidic channels 16, 18, 20formed therein. Incident excitation light, represented by arrows 22, isdirected through the incident surface 12 at channel 18, light passingthrough channel 18 toward an opposite surface 14 of the chip 10 isrepresented by arrows 24, and light reflected or refracted towardadjacent channels 16, 20 is represented by arrows 26, 28, respectively.As shown in FIG. 2, emission light from the channel 18 at which theexcitation light 22 is directed is represented by arrows 30. A portionof the emission light 30 is directed at the adjacent channels 16 and 20,as represented by arrows 32 and 34, respectively. The light 26, 32incident on channel 16 and the light 28, 34 incident on channel 20 maycause emissions from channels 16 and 20, as represented by arrows 36 and38, respectively. A portion of the emission light 36, 38 from theadjacent channels 16, 20, respectively, will be directed toward theincident surface 12, as represented by arrows 40 and 42, toward thedetector (not shown), thereby causing an inaccurate signal strengthsignal from the channel 18 and/or false signals from the adjacentchannels 16, 20.

Also, much of the emission light 30 from the channel 18 will be directedtoward surface 14 and will not be detected by the detector that is abovesurface 12, thus resulting in a relatively weak emission signal fromchannel 18.

Accordingly, a need exists for a microfluidic chip having means forpreventing thermal and optical cross-talk between adjacent microfluidicchannels and further for capturing more of the omni-directional emissionlight from a channel.

SUMMARY

The present invention encompasses systems and methods for providing anoptical and/or thermal barrier between adjacently oriented microfluidicchannels to reduce or prevent optical and/or thermal cross-talk betweenthe adjacent channels. Other aspects of the invention encompass systemsand methods for providing reflective features that reflect back toward adetector at least a portion of the light passing through or emanatingfrom a microfluidic channel.

Accordingly, aspects of the invention are embodied in a microfluidicdevice comprising at least first and second microfluidic channels and abarrier channel interposed between at least a portion of the firstmicrofluidic channel and a portion of the second microfluidic channel.The barrier channel contains a material that is of lower refractiveindex than a material forming the microfluidic channels and isconfigured to reduce transfer of heat and/or light between themicrofluidic channels.

According to another aspect, the microfluidic device comprises aplurality of microfluidic channels and a barrier channel interposedbetween at least a portion of each pair of adjacent microfluidicchannels.

According to another aspect, at least one segment of the firstmicrofluidic channel is substantially parallel to at least one segmentof the second microfluidic channel. The barrier channel is interposedbetween the parallel segments of the first and second microfluidicchannels and is substantially parallel to the microfluidic channels.

According to another aspect, the material forming the microfluidicchannels comprises glass. In other embodiments, the material forming themicrofluidic channels is plastic.

According to another aspect, the barrier channel is filled with a gasselected from the group consisting of air, argon, carbon dioxide,krypton, SF6, or any mixture of two or more of air, argon, carbondioxide, krypton, or SF6.

According to another aspect, the barrier channel has one or more channelsides which form angles to adjacent microfluidic channel sides such thatthe barrier channel side transversely reflects light arriving at thebarrier side from the adjacent microfluidic channel.

According to another aspect, the barrier channel is trapezoidal in axialcross-section and includes opposed parallel sides and opposed angledsides. The angled sides face the first and second microfluidic channels.According to another aspect, the angled sides are oriented at an angleof approximately 45 degrees to the parallel sides.

According to another aspect, at least a portion of a surface of thedevice comprises a reflecting surface configured to cause light passingthrough or emanating from the microfluidic channels toward thereflecting surface to be redirected by total internal reflection.According to another aspect, the reflecting surface comprises surfacefacets oriented at angles with respect to each other. According toanother aspect, the facets are oriented at an angle of approximately 45degrees to each other.

According to another aspect, the microfluidic device further comprisesreflecting channels disposed adjacent to at least a portion of each ofthe microfluidic channels. The reflecting channels are configured tocause light passing through or emanating from the microfluidic channelstoward the reflecting channels to be redirected by total internalreflection.

According to another aspect, the reflecting channels comprise twochannels, each being triangular in axial cross-section, disposedadjacent to at least a portion of each of said first and secondmicrofluidic channels. According to another aspect, the two channels arearranged side-by-side with the base sides of the triangularcross-sections co-planar with one another and an apex of each triangularcross-section contacting an apex of the adjacent triangularcross-section.

According to another aspect, the microfluidic device includes one ormore functional segments of the first and second microfluidic channels,and barrier channels are omitted from between the microfluidic channelsat each functional segment.

Other aspects of the invention are embodied in a microfluidic devicewhich comprises at least first and second microfluidic channels. Anoptical isolation element is embedded in the microfluidic device and isinterposed between at least a portion of the first microfluidic channeland a portion of the second microfluidic channel. The optical isolationelement is adapted to reduce transfer of light between the microfluidicchannels at the portions of the microfluidic channels between which theoptical isolation element is interposed. A signal enhancement element isembedded in the microfluidic device and is disposed adjacent to at leasta portion of each of the microfluidic channels. The signal enhancementelement is configured to reflect light passing through or emanating fromthe microfluidic channels and impinging on the signal enhancementelement.

According to another aspect, the microfluidic device includes aplurality of microfluidic channels, and an optical isolation element isinterposed between at least a portion of each pair of adjacentmicrofluidic channels.

According to another aspect, the microfluidic device includes one ormore functional segments of the first and second microfluidic channels,and the optical isolation element and the signal enhancement element areomitted from between the microfluidic channels at each functionalsegment.

According to another aspect, the optical isolation element comprisesmetal film, and the signal enhancement element comprises metal film.These metal films are preferably made of aluminum or silver. Othersuitable metals include gold, platinum and nickel.

The above and other aspects and embodiments of the present invention aredescribed below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate various embodiments of the presentinvention. In the drawings, like reference numbers indicate identical orfunctionally similar elements.

FIG. 1 is a partial, transverse cross-section of a microfluidic devicein accordance with the prior art.

FIG. 2 is a partial, transverse cross-section of a microfluidic devicein accordance with the prior art.

FIG. 3 is a partial, transverse cross-section of a microfluidic devicein accordance with embodiments of the invention including features forlimiting optical cross-talk between channels of the device and showingexcitation light rays incident on a channel and redirection of lightdeflected from the channel toward adjacent channels.

FIG. 4 is a partial, transverse cross-section of a microfluidic devicein accordance with the embodiments of the invention including featuresfor limiting optical cross-talk between channels of the device andshowing emission light rays emanating from a channel and redirection oflight emitted from the channel toward adjacent channels.

FIG. 5 is a partial, transverse cross-section of a microfluidic devicein accordance with the embodiments of the invention including featuresfor limiting optical cross-talk between channels of the device andfeatures for reflecting light internally from a surface of the device bytotal internal reflection.

FIG. 6 is an alternative embodiment of the microfluidic device of FIG.5.

FIG. 7 is a further alternative embodiment of the microfluidic device ofFIG. 5.

FIG. 8 is a partial plan view of a microfluidic device in accordancewith embodiments of the invention including functional regions anddetecting regions with optical isolation elements and signal enhancementelements.

FIG. 8A is a transverse cross-section along the line A-A of FIG. 8.

FIG. 8B is a transverse cross-section along the line B-B of FIG. 8.

FIG. 9 is a partial plan view of an alternative embodiment of amicrofluidic device including functional regions and detecting regionswith optical isolation elements and signal enhancement elements.

FIG. 9A is a transverse cross-section along the line A-A of FIG. 9.

FIG. 9B is a transverse cross-section along the line B-B of FIG. 9.

FIG. 10 is a partial, transverse cross-section of a microfluidic devicein accordance with other embodiments of the invention including featuresfor limiting optical cross-talk between channels of the device andshowing emission light rays emanating from a channel and redirection oflight away from the detector.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A microfluidic chip embodying aspects of the present invention isindicated by reference number 10 a in FIGS. 3 and 4, which shows aschematic representation of a partial transverse cross-section of themicrofluidic chip 10 a. Microfluidic chip 10 a may be made of clearglass or polymer and includes a number of microfluidic channels 16, 18,20 formed therein and which may be parallel along portions of theirlengths. The microfluidic chip 10 a is illustrated in FIGS. 3 and 4having three microfluidic channels. However, more or fewer microfluidicchannels can be used. Extending between at least portions of themicrofluidic channels 16, 18, 20, and oriented generally parallelthereto, are barrier channels 21. Barrier channels 21 are configured toreduce heat and/or light transfer between adjacent microfluidicchannels. More specifically, to reduce heat transfer between adjacentmicrofluidic channels, each barrier channel 21 may be filled with asubstance having relatively poor thermal conductivity. Exemplarysubstances exhibiting relatively poor thermal conductivity includegases, such as, air, argon, carbon dioxide, krypton, SF6, or any mixtureof two or more of air, argon, carbon dioxide, krypton, or SF6.Accordingly, the barrier channel 21 so-configured effects adiscontinuity in the thermal transfer path between adjacent microfluidicchannels to thereby reduce thermal transfer (i.e., thermal crosstalk)between the adjacent microfluidic channels. Thus, barrier channels 21function as thermal isolation elements which create a degree of thermalisolation of each of the microfluidic channels 16, 18, 20 by limitingthe amount of thermal energy transfer between adjacent microfluidicchannels.

Furthermore, to reduce light transfer between adjacent microfluidicchannels, the barrier channels 21 may have angled sides 23 and may befilled with a substance having a lower index of refraction than thematerial of which the microfluidic chip 10 a is formed. Again, suitablesubstances exhibiting relatively low indices of refraction includegases, such as, air, argon, carbon dioxide, krypton, SF6, or any mixtureof two or more of air, argon, carbon dioxide, krypton, or SF6.

As shown in FIG. 3, incident excitation light, represented by arrows 22,is directed through the incident surface 12 of microfluidic chip 10 a atchannel 18, light passing through channel 18 toward an opposite surface14 of the chip 10 a is represented by arrows 24, and light reflected orrefracted toward adjacent channels 16, 20 is represented by arrows 26,28, respectively. As shown in FIG. 4, emission light from the channel18, at which the excitation light 22 is directed, is represented byarrows 30. A portion of the emission light 30 is directed at theadjacent channels 16 and 20, as represented by arrows 32 and 34,respectively.

However, instead of impinging on channels 16 and 20, the light 26, 32directed toward the channel 16 and the light 28, 34 directed toward thechannel 20 encounter an intervening barrier channel 21. The angled sides23 of the barrier channel 21, combined with the reduction in the indexof refraction at the interface of channel 21 and the chip body, causelight impinging on the sides 23 to deflect by total internal reflectionin directions away from adjacent channels 16 and 20. In one embodiment,barrier channels 21 have a trapezoidal shape with a top side and bottomside that are parallel to each other and to the incident surface 12 andopposed angled sides 23 that are oriented at 45 degrees to the top andbottom sides, as shown, to cause the light redirected by the barrierchannel to be directed toward the incident surface 12, as represented byarrows 26 a, 28 a (FIGS. 3) and 32 a, 34 a (FIG. 4).

Thus, barrier channels 21 also function as optical isolation elementswhich create a degree of optical isolation of each of the microfluidicchannels 16, 18, 20 by limiting the amount of optical signal transfer(i.e., optical crosstalk) between adjacent microfluidic channels.

Another embodiment of a microfluidic chip embodying aspects of thepresent invention is indicated by reference number 10 b in FIG. 5, whichshows a schematic representation of a partial transverse cross-sectionof the microfluidic chip 1 Ob. Microfluidic chip 10 b is, in manyrespects, similar to microfluidic chip 10 a shown in FIGS. 3 and 4 andincludes, for example, microfluidic channel 18 and barrier channels 21with angled sides 23. Microfluidic chip 10 b differs from microfluidicchip 10 a, however, in that the bottom 14 b of microfluidic chip 10 b isnot flat as is bottom surface 14 of microfluidic chip 10 a. Instead, thebottom 14 b of microfluidic chip 10 b is defined by a plurality offacets 15, 17 oriented at angles to each other. As shown in FIG. 5, thefaceted surface of bottom 14 b causes light passing through or emittedfrom channel 18 toward bottom 14 b (as indicated by arrow 24) to beredirected at the facets 15, 17 by total internal reflection. In oneembodiment, the facets 15, 17 are oriented at approximately 45 degreesrelative to incident surface 12, as shown, to cause at least a portionof the light 24 redirected by the facets 15, 17 to be directed towardthe incident surface 12 as represented by arrows 24 a, 24 b.

Thus, the facets 15, 17 of microfluidic chip 10 b function as signalenhancement structures because they reflect at least a portion of thelight passing through or emitted from the microfluidic channel 18 backtoward the incidence surface 12 so that light can be detected, thusincreasing the strength of—and thereby enhancing—the detected opticalsignal.

A further embodiment of a microfluidic chip embodying aspects of thepresent invention is indicated by reference number 10 c in FIG. 6, whichshows a schematic representation of a partial transverse cross-sectionof the microfluidic chip 10 c. Microfluidic chip 10 c includesmicrofluidic channels 18 c, 20 c having the same configuration as thebarrier channels 21. In the illustrated embodiment, microfluidicchannels 18 c, 20 c, like barrier channels 21, have a trapezoidal shapewith a top side and bottom side that are parallel to each other and tothe incident surface 12 and opposed angled sides that are oriented atapproximately 45 degrees to the top and bottom sides. Forming themicrofluidic channels 18 c, 20 c with the same configuration as thebarrier channels 21 may be desirable as it may simplify manufacture tohave all channels identically configured.

Another embodiment of a micro-fluidic chip embodying aspects of thepresent invention is indicated by reference number 10 d in FIG. 7, whichshows a schematic representation of a partial transverse cross-sectionof the microfluidic chip 10 d. Microfluidic chip 10 d includes a bottomportion 14 d having facets 15 d, 17 d disposed only beneath themicrofluidic channels 18, 20. In the illustrated embodiment, facets 15d, 17 d are oriented at about 45 degrees to the incident surface 12. Amicrofluidic chip configuration such as 10 d may have a reduced mass ascompared to microfluidic chip configuration 10 b shown in FIG. 5, yetmicrofluidic chip 10 d would retain the ability to reflect light passingthrough or emitted from the microfluidic channels 18, 20 by totalinternal reflection.

A further embodiment of a microfluidic chip embodying aspects of thepresent invention is indicated by reference number 50 in FIGS. 8, 8A,and 8B. Microfluidic chip 50 includes a number of microfluidic channels52 (four channels in the illustrated non-limiting embodiment), and themicrofluidic chip 50 is divided into optical interrogation regions 60and functional regions 62. As implied by the name, the opticalinterrogation regions 60 are sections of the lengths of the microfluidicchannels 52 at which the channels are optically interrogated, such as byan optical detector adapted to detect chemiluminescence or to generatean optical excitation signal and detect emitted fluorescence. As shownin FIG. 8A, which shows the optical interrogation region 60 incross-section, the optical interrogation regions 60 are characterized bybarrier channels (i.e., optical isolation channels) 64 interposedbetween adjacent microfluidic channels 52 for preventing opticalcross-talk between the adjacent channels. In one embodiment, barrierchannels 64 have a trapezoidal shape with a top side and bottom sidethat are parallel to each other and to the top (incident) surface 54 andopposed angled sides that are oriented at approximately 45 degrees tothe top and bottom sides, as shown, to cause the light redirected by thebarrier channel 64 to be directed toward the top surface 54. In otherembodiments, the barrier channel 64 could be triangular in axialcross-section. In other embodiments, the barrier channel 64 is angledsufficiently such that the impinging light 26, 32 and 28, 34 strikes thebarrier channel 64 at an angle (with respect to the normal of thebarrier channel surface) that is greater than the critical angle. Thecritical angle is equal to the arcsine of the ratio of the indices ofrefraction, where the ratio is the index of refraction of the materialwithin the barrier channel divided by the index of refraction of thesubstrate material.

The optical interrogation region 60 further includes signal enhancementelements in the form of channels 70, 72 arranged in a side-by sideconfiguration below each of the microfluidic channels 52. In preferredembodiments, channels 70, 72 have opposed sides 74, 76 arranged atangles to each other and are filled with a substance having a lowerindex of refraction than the material of which the microfluidic chip 50is formed, such as, air, argon, carbon dioxide, krypton, SF6, or anymixture of two or more of air, argon, carbon dioxide, krypton, or SF6.

Accordingly, sides 74, 76 will reflect light passing through or emittedfrom channels 52 by total internal reflection, and will redirect thelight upwardly toward top surface 54, as indicated by arrows 78, 80, 82.

In the illustrated embodiment, channels 70, 72 are triangular in axialcross-section with sides 74, 76 oriented at approximately 45 degreesrelative to base sides 75, 77 which are substantially co-planar andparallel to top surface 54. In a preferred embodiment, channels 70, 72contact each other at apexes 71, 73. In other embodiments, the channels70, 72 could also be trapezoidal in axial cross-section provided the 45degree surfaces 74, 76 remain beneath the microfluidic channel 52.

As an alternative to channels 70, 72, microfluidic chip 50 may includesignal enhancement features comprising a faceted bottom surface as shownin FIGS. 5 and 7. Similarly, facets 15, 17 of microfluidic chip 10 b ofFIG. 5 and facets 15 d and 17 d of microfluidic chip 10 d of FIG. 7 maybe replaced by internal optically-deflecting channels, such as channels70, 72, of microfluidic chip 50 of FIG. 8A.

Functional regions 62 are sections of the lengths of microfluidicchannels 52 at which the channels 52 are not optically interrogated.Functional regions 62 may simply be extents of the channels at whichmaterial is conveyed from one portion of the microfluidic chip toanother, or they may comprise extents of the channels at which otherprocessing steps, e.g., heating, mixing, or some combination of theseand/or other steps, are performed. As shown in FIG. 8B, which shows thefunctional region 62 in cross section, because there is no opticalinterrogation in the functional regions 62, there is no need for opticalisolation elements (e.g., barrier channels 64) or signal enhancementelements (e.g., channels 70, 72). If heating is performed in afunctional region 62, it may be desirable to provide thermal isolationbarrier channels between adjacent microfluidic channels 52 to prevent,or at least limit, thermal cross-talk between adjacent microfluidicchannels. Under such circumstances in which the barrier channels areprovided to perform a thermal isolation function, but not an opticalisolation function, such channels need not have angled sides so as toeffect total internal reflection, but need only have a suitable size andshape (e.g., rectangular or circular), and be filled with a materialhaving relatively low thermal conductivity, to provide an effectivethermal barrier between adjacent microfluidic channels.

A further embodiment of a microfluidic chip embodying aspects of thepresent invention is indicated by reference number 100 in FIGS. 9, 9A,and 9B. Microfluidic chip 100 includes a number of microfluidic channels102 (four channels in the illustrated non-limiting embodiment), and thechip 100 is divided into sequential optical interrogation regions 110and functional regions 112. As shown in FIG. 9A, which shows the opticalinterrogation region 110 in cross-section, the optical interrogationregions 110 are characterized by optical isolation elements 114interposed between adjacent microfluidic channels 102 for preventingoptical cross-talk between the adjacent channels. In one embodiment,optical isolation elements 114 comprise metal film segments (e.g.,aluminum or silver) embedded into the chip 100 between pairs of adjacentmicrofluidic channels 102 and oriented so as to be transverse (e.g.,substantially perpendicular) to a would-be straight-line optical pathextending from one channel 102 to the adjacent channel 102. Other metalssuitable for these metal films include gold, platinum and nickel.

The optical interrogation region 110 further includes signal enhancementelements 116 disposed below each of the microfluidic channels 102,opposite a top surface 104 at which optical detection occurs. In oneembodiment, signal enhancement elements 116 comprise metal film segments(e.g., aluminum or silver) embedded into the chip 100 below microfluidicchannels 102 and oriented so as to be parallel to top surface 104. Othermetals suitable for these metal films include gold, platinum and nickel.

As shown in FIG. 9B, which shows functional regions 112 incross-section, optical isolation elements (e.g., metal film segments114) and signal enhancement elements (e.g., metal film segments 116) areomitted from functional region 112.

Another embodiment of a microfluidic chip embodying aspects of thepresent invention is indicated by reference number 10 e in FIG. 10,which shows a schematic representation of a partial transversecross-section of the microfluidic chip 10 e. Microfluidic chip 10 e is,in many respects, similar to microfluidic chip 10 a shown in FIGS. 3 and4 and includes, for example, microfluidic channels 16, 18, 20, incidentsurface 12, and bottom surface 14. Microfluidic chip 10 e differs frommicrofluidic chip 10 a, however, in that the barrier channels 21 e ofchip 10 e are inverted, or rotated by approximately 180 degrees abouttheir longitudinal axes, as compared to barrier channels 21 ofmicrofluidic chip 10 a. Accordingly, refracted or emitted light fromchannel 18, such as emitted light represented by arrows 30, that isdirected at the adjacent channels 16 and 20, as represented by arrows 32and 34, respectively, is redirected by the barrier channel 21 e towardthe bottom surface 14, as represented by arrows 32 e, 34 e, and awayfrom a detector.

While the present invention has been described and shown in considerabledetail with disclosure to certain preferred embodiments, those skilledin the art will readily appreciate other embodiments of the presentinvention. Accordingly, the present invention is deemed to include allmodifications and variations encompassed within the spirit and scope ofthe following appended claims.

1-21. (canceled)
 22. A microfluidic device comprising: at least onemicrofluidic channel; wherein at least a portion of a surface of themicro fluidic device comprises a reflecting surface configured to causelight passing through or emanating from the at least one microfluidicchannel toward said reflecting surface to be redirected by totalinternal reflection.
 23. The microfluidic device of claim 22, whereinsaid reflecting surface comprises surface facets oriented at angles withrespect to each other.
 24. The microfluidic device of claim 23, whereinthe facets are oriented at an angle of approximately 45 degrees withrespect to each other.
 25. The microfluidic device of claim 22, whereinthe at least a portion of the surface of the micro fluidic devicecomprising a reflecting surface is located only beneath the at least onemicrofluidic channel.
 26. The microfluidic device of claim 22, whereinthe material forming said microfluidic device comprises glass.
 27. Themicrofluidic device of claim 23, wherein the surface facets function assignal enhancement structures.
 28. The microfluidic device of claim 22wherein the reflecting surface is opposite a flat surface of themicrofluidic chip.